For ever, i.e. all the time of his life, or, at least, till the year of jubilee. See on Exodus 21:6. Unto thy maid-servant thou shalt do likewise, i.e. either dismiss her honourably, and with plenty of provisions; or engage her to perpetual servitude in the same manner, and by the same rites; whence it appears that this case differs from that Exodus 21:7, and that the maid-servant there was taken in upon other and better terms than this here.
Related Commentaries of Deuteronomy 15:17
Deuteronomy 15:17
17 Then thou shalt take an aul, and thrust it through his ear unto the door, and he shall be thy servant for ever. And also unto thy maidservant thou shalt do likewise.